This invention is generally concerned with sheet feeding apparatus and more particularly with apparatus for feeding sheets respectively supported on an edge thereof, whereby such sheets are fed in an upright orientation thereof.
In U.S. Pat. No. 4,302,000 for Apparatus For Separating A Letter Stack, issued Nov. 24, 1981 to Warner Frank, there is shown sheet feeding structure wherein sheets are fed on their edges from a stack of sheets. In the Patent, a spring loaded supporting wall at the upstream end of the stack is intermittently moved in a downstream path of travel by a switch actuated drive system, and belt structure at the downstream end of the stack feeds the sheets from the stack. A pair of springs are provided for spring loading the upstream sheet supporting wall, and the drive system includes an arm which compresses the springs against the wall for moving the same whenever the force being exerted by the stack against the belt structure does not exceed a value which causes the drive system's switch to be actuated. The spring structure is provided to ensure that the force exerted against the belt structure, which reliably feeds sheets only when that force is within a predetermined range of values, will not attain unduly high values.
It has been found that although the spring structure shown in the Patent generally enhances the feeding reliability of the belt structure, the mass of the stack normally includes unavoidable air pockets which tend to dampen the effect of the springs. Moreover, since the forces exerted by the springs are unevenly relieved when thick sheets are fed from the stack, and a given sheet may be of varying thickness along its feeding length, the forces exerted on the belt structure may vary considerably as a given sheet is being fed from the stack. As a result, the drive system tends to require continuous adjustment to achieve reliable sheet feeding with sheets of different thicknesses. Accordingly:
An object of the invention is to provide improved apparatus for feeding sheets of different thickness;
Another object is to provide apparatus for feeding sheets from a stack, including improved structure for controlling the force exerted by the stack against a guide wall; and
Another object is to provide sheet feeding apparatus including means for exerting a substantially constant resultant force against respective sheets fed from the stack.